The UN estimates that there will be 9.9 billion people on this planet by 2075. They'll all need to eat, as do the many people who are going hungry around the world today.

One challenge in the fight against hunger, today and tomorrow, is food waste.

And it's a very big challenge. According to a new study from the UK-based Institute of Mechanical Engineers, as much as half of the world's food (or two billion tonnes a year) is wasted.

The report, 'Global Food: Waste Not, Want Not', says between 30 and 50 per cent of food produced around the world each year goes to waste through a combination of inefficient farming (especially in developing nations), and bad market and consumer habits (mainly in developed nations).

In less-developed countries, the report says, waste tends to occur at "the farmer-producer end of the supply chain," as a result of inefficient harvesting, a lack of local transportation, and poor infrastructure.

But what about developed nations, where our farming methods have money and infrastructure behind them?

The Institute's report says "characteristics associated with modern consumer culture" are the culprits: overly strict best-before dates on food, two-for-one style offers that encourage people to buy more than they need, and people's desire for perfect-looking produce all lead to food waste.

That last point is worth thinking about: the study's authors found that "major supermarkets, in meeting consumer expectations, will often reject entire crops of perfectly edible fruit and vegetables at the farm because they do not meet exacting marketing standards for their physical characteristics."

In the UK, up to 30 per cent of the vegetable crop "is never harvested as a result of such practices," the report says. It estimates that throwing away "ugly" produce leads to 1.6 million tonnes of food waste around the world every year.

The obvious consequence is a lack of available nutrition for people. But the report also highlights the cost in terms of resources and energy: "Wasting food means losing not only life-supporting nutrition but also precious resources, including land, water and energy."

An estimated 550 billion cubic metres of water is wasted on crops that are never eaten, according to the authors, and the demand for water in food production could rise to 10 to 13 trillion cubic metres a year by 2050.

The goal of the study is to engage organizations like the United Nations, the world's governments, and NGOs in the challenge of reducing food waste.

Dr. Tim Fox, head of energy and environment at the Institution of Mechanical Engineers, spoke to the BBC's Today programme on Thursday.

"As water, land and energy resources come under increasing pressure from competing human demands, engineers have a crucial role to play in preventing food loss and waste by developing more efficient ways of growing, transporting and storing foods.

"But in order for this to happen governments, development agencies and organizations like the UN must work together to help change people's mindsets on waste and discourage wasteful practices by farmers, food producers, supermarkets and consumers."

Some experts have noted that the study, while raising important issues, may not have come to entirely accurate conclusions.

"Based on years of research," Toine Timmermans from Wageningen University and Research Centre told the BBC, "I find the conclusion about the amount of food waste (1.2-2 billion tonnes) unrealistically high."

And environmental journalist Matt McGrath points out that one expert in the field says "there was no absolutely reliable global data on the level of waste," and that the report "draws heavily on work carried out over a number of years for the Food and Agriculture Organization of UN."

The report recommends that farmers and food producers in the developing world be better trained in engineering and in ways to reduce waste.

It also calls on governments in developed nations to "devise and implement policy that changes consumer expectations."

"These should discourage retailers from wasteful practices that lead to the rejection of food on the basis of cosmetic characteristics, and losses in the home due to excessive purchasing by consumers."

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